Characterization of a Double Metal Cyanide (DMC)-Type Catalyst in the Polyoxypropylation Process: Effects of Catalyst Concentration

The alkaline catalysts commonly applied to alkoxylation are characterized by a limited spectrum of activity caused by an irreversible termination of the polyether chains. The presented results show that double metal cyanide (DMC) catalysts reduce or eliminate the aforementioned adverse rearrangement of hydroxyl groups. Moreover, DMC catalysts indicate high activity at low concentrations (ppm range), as expressed by high polymerization rates. It was demonstrated that decreased concentrations of DMC catalyst irreversibly influence its reactivity and the dispersity of the obtained products, as exemplified by the production and determination of selected polyoxypropylenediols at different concentrations of the catalyst. Because of their unique advantages, the DMC catalysts are a very attractive alternative to conventional alkaline catalysts for the polyaddition of oxiranes. The phenomenon was discussed and explained by an alteration of reaction rate coefficients at subsequent polyaddition stages.